A significant trend throughout integrated circuit (IC) development is the downsizing of IC components. As the size reduces, the performance requirements become more stringent. As devices continue to shrink in size, the channel region also continues to shrink as well. For metal-oxide-semiconductor field effect transistors (MOSFETs), increased performance requirements have generally been met by aggressively scaling the length of the channel region. However, such a short channel length faces high electric field and manufacturing limits.
Generally, threshold voltage is directly related to the doping concentration in a channel. As the length of a channel continues to shrink, diffusion of dopants becomes much harder to control. There are various thermal processes throughout a semiconductor manufacturing. For example, after dopants are implanted into a substrate, a thermal process is used to activate the dopants. In addition, after a deposition, a thermal process is required to repair broken bonding at an interface. However, these thermal processes cause dopant diffusion in an unintentional way. Diffused dopants may penetrate into a channel region. The electrical properties, such as threshold voltage, are altered and deviated from a predetermined value. This causes uniformity between each device and is a severe problem in circuit design.
In addition, shorter channel lengths suffer from fluctuation of higher implantation concentration and depth. This situation is significant for boron, which has a relatively lower atomic weight and a longer diffused length. As a result, it is difficult for IC designers to control the doped profile. The unintentional dopant diffusion induces a poor threshold voltage and saturation current uniformity.